Insulated armature construction and method

ABSTRACT

An armature including a sleeve of insulating material bonded in place between the armature shaft and the armature laminations. The insulating sleeve may extend under the commutator if desired. A method of providing this armature is also described which comprises holding the laminations, the sleeve and the shaft in their relative positions and injecting a bonding material between the sleeve and the shaft and between the sleeve and the laminations.

United States Patent Bednarski [54] INSULATED ARMATURE CONSTRUCTION ANDMETHOD [72] inventor: Thaddeus E. Bednarski, Timonium, Md.

[73] Assignee: The Black and Decker Manufacturing Company, Towson, Md.

221 Filed: Nov.2l,1969

211 Appl.No.: 878,825

[52] U.S. Cl ..310/43, 310/261 [51] Int. Cl. ..H02k 1/04 [58] Field ofSearch ..310/42, 43, 47, 50, 265, 216,

[56] References Cited UNITED STATES PATENTS 2,541,047 2/1951 Frisbie eta1. ..310/235 2,818,517 12/1957 Loosjes ..310l26l X 3,447,011 5/1969Amrein et a1. .....310/236 X 3,471,731 10/1969 Pratt et al. ..310/235 X1 1 Feb. 1, 1972 FOREIGN PATENTS OR APPLICATIONS 979,009 1/1965 GreatBritain ..3 10/43 Primary Examiner-D. F. Duggan Attorney-Leonard Bloom,Joseph R. Slotnik and Edward D. Murphy ABSTRACT An armature including asleeve of insulating material bonded in place between the armature shaftand the armature laminations. The insulating sleeve may extend under thecommutator if desired. A method of providing this annature is alsodescribed which comprises holding the laminations, the sleeve and theshaft in their relative positions and injecting a bonding materialbetween the sleeve and the shaft and between the sleeve and thelaminations.

8 Claims, 2 Drawing Figures PATENTEDFEB H972 3.639.789

PRESSURIZED ADHESIVE I mvmon THADDEUS E. BEDNARSKI TO VACUUM SYSTEM 2624 BY My ATTORNEY INSULATED ARMATURE CONSTRUCTION AND METHOD Thisinvention relates to double insulated armature shafts and isparticularly directed to a double insulated construction which is bothimproved and less expensive to manufacture.

One present method of providing insulation between the shaft of anelectric motor and the stack of laminations in which the armaturewindings are placed is based on the injection and molding in place of amaterial which performs both the functions of bonding the laminations tothe shaft and of insulating the laminations from the shaft. It is\difficult to obtain materials which adequately meet all of therequirements of this process without excessive cost. An even moresignificant expense of this process is the fact that the material mustbe molded in place within a highly complex press which holds the variouselements in the proper location and applies suitable heat and pressureso that an injected resin is molded in place. Suitable presses forperfonning this operation are extremely expensive; in addition, only afew units can be processed at a time so that, for mass production, largenumbers of the presses are required with a consequent increase in thecapital investment required.

An alternative to this method is that of molding a sleeve around thearmature shaft, grinding it to an appropriate size and pressing it intothe center bore in the stack of laminations. While this processdecreases the expense of the press required for molding the sleeve, thetolerance requirements of the pressing operation are extremely high.These requirements apply to the size of the center bore, the size of themolded sleeve and the relative position of the sleeve and the stack asthe pressing is performed. Tolerance limitations on these steps areusually on the order of 0.001 inch or even less. Massproduction toolingwhich can maintain these tolerances over extended periods of qualityproduction is extremely expensive. It is a primary purpose of thisinvention toprovide a new armature construction which avoids thesedifficulties and the consequent expense while at the same time providingimproved results.

It is accordingly an object of this invention to provide a new andimproved insulated armature.

Another object of this invention is the provision of a new and improvedarmature which is less susceptible to breakdown of the insulationbetween the armature shaft and the laminations.

Another object of this invention is the provision of a new and improvedmethod of constructing armatures which is less complicated and lessexpensive than previous methods.

Further objects and advantages of this invention will become apparent asthe description and illustration thereof ensue.

Briefly, in accord with one embodiment of this invention, an armaturefor an electric motor is provided which includes a rotor having aplurality of windings and a central bore, a shaft located within thebore for providing a power output, an insulating sleeve disposed betweenthe rotor and the shaft and adhesive layers respectively affixing therotor to the sleeve and the sleeve to the shaft. In a particularembodiment, the sleeve comprises a glass cylinder and the adhesivelayers are of sufficient thickness to compensate for thermal andmechanical stresses between the rotor and the sleeve and between thesleeve and the shaft. In accord with another specific embodiment, thesleeve may comprise a paper cylinder.

This invention will thus be understood from a consideration of thefollowing description and accompanying drawings in which:

FIG. 1 is a plan view, partially in cross section, of an annatureconstructed in accord with the present invention; and

FIG. 2 is a cross-sectional view of apparatus for performing the methodin accord with this invention.

In FIG. 1, an armature I is illustrated which comprises a stack oflaminations 11 having a plurality of slots 12 in which coils 13 ofinsulated wire are wound in accord with conventional practice. Each coilis attached to a conductive bar 14 of a commutator 15, the particulararmature illustrated being designed for use in a universal motor.

The laminations 11 are provided with a central bore 16 in which isdisposed a shaft 17. In use, an electromagnetic torque applied to thewindings causes the rotor to rotate and a power output is derived fromone end of the shaft 17 which is located within the bore 16.

In accord with the present invention, the shaft is insulated from therotor stack by means of a sleeve 18 of insulating material whichsurrounds the shaft and extends under the entire length of the stack.The sleeve is affixed to the shaft 17 and to the stack 11 by means ofadhesive layers 19 and 20. For example, in a preferred embodiment ofthis invention, the sleeve 18 comprises a glass cylinder while theadhesive layers comprise a room temperature vulcanizing silicon rubber.

A particularly significant advantage of this invention is derived fromthe method of assembly. Specifically, as previously noted, other methodsrequire very complex and expensive equipment, either for holding theparts in place during molding or for meeting the tolerance requirementsof a pressing operation. The armature of the present invention can beconstructed in simple, inexpensive apparatus which can readily beadapted to the manufacture of large quantities. For example, FIG. 2illustrates schematically a suitable fixture for the performance of themethod of this invention. The supporting structure 21 includesrespective openings 22, 23 and 24 for receiving the shaft, sleeve andlaminations. A cover member 25 is clamped in place to secure thelaminations and to hold the shaft and sleeve in alignment. Vacuum lines26 are preferably used to prevent the entrapping of air at the base ofthe unit; appropriate means may of course be provided to seal off theseopenings when the adhesive is introduced.

The adhesive is supplied from a reservoir of liquid adhesive. A valve 27supplies the adhesive to nozzles 28 and 29 which respectively inject theliquid adhesive into the spaces between the laminations and the sleeveand between the sleeve and the shaft. After the adhesive is introduced,curing may be performed either by time alone or by the application ofheat to increase the speed of curing.

Even if a source of heat is provided to assist in curing the adhesive,the fixture and tooling for performing this method are much simpler thanthat required by previous methods. For example, thetolerance'requirements for the relative size and position of the threeelements need only be maintained within several thousandths of an inch.Although this is still a relatively small space, the difference in thetooling required to maintain this tolerance as compared to that of lessthan 0.001 inch may reduce the cost by a factor of one-third toone-fifth. A similar comparison also applies when considering thisequipment as compared to'that required for performing molding of amaterial which must function both as an adhesive and as an insulator.

As previously noted, the subject invention not only enables the cost ofmanufacture to be substantially reduced, but it also provides a moreeffective insulative barrier than previous methods. Specifically, if thesingle layer of previous constructions is provided, a breakdown in thatmaterial which occurs due to a particular cause is frequently of a typewhich can readily propagate across the width of the material. This isdue to the fact that the cause of the initial breakdown may continue toaffect the-same material in the same way. In a construction according tothe present invention, however, this possibility is avoided becausethere are two different material arranged in three layers between theshaft and the stack. Thus, a cause of failure in one of the layers isunlikely to have any effect at all on the adjacent layer of the othermaterial. For example, if breakdown of the polymeric adhesive materialoccurs due to age in either of the adhesive layers, it may propagaterapidly across the width of that layer but it will not propagate throughthe sleeve since the sleeve is chemically different and is not affectedby the same conditions. On the other hand, if a rupture occurs in thesleeve, it will not affect the adhesive layers on either side since theadhesive is a relatively resilient material and will withstand therupturing stress. Thus, the insulation provided by the illustratedconstruction is substantially more effective than that provided byprevious constructions.

' and the adhesive material is a room temperature vulcanizing rubber.This particular embodiment is of interest due t'othe fact that thedielectric strength of glass is so highthat the insulation requirementssuch as, for example, those of- Underwriters Laboratories, Inc., aremore than fulfilled by the glass cylinder itselfand any insulatingeffect provided by the rubber is, in effect, a bonus. A potentialdifficulty with this embodiment is the possibility that the glass maybreak. In accord with this invention, this is overcome by providing asufficiently thick and sufficiently resilient layer of adhesive on eachside of the sleeve'so that any stresses introduced between the shaft andthe stack which might tend to fracture the glass are taken up by theadhesive. For example, these stresses may be either thermal, due to adifference in the amount of expansion under heat of the glass cylinderas compared to the metal stack and shaft, or mechanical, due to thetwisting moment between therotor stack and the shaft.

Another embodiment of this invention which also enjoys the advantageslisted above is that in which the'sleeve is made of paper of asufficient thickness and dielectric strength so that the electricalinsulative requirements are met. In this embodiment, since the sleeveisnot susceptible to breaking, even wider tolerance in manufacture can bepermitted since the adhesive need only be sufficient to bond theelements together. Thus, the sleeve can be positioned rather looselyaround the shaft and the adhesive can be injected under sufficientpressure to insure that all of the spaces in both annular openingsselected if desired. it is also noted that, to meet specificrequirements, various modifications in the properties of these materialsmay be desired. For example, by providing a certain amount of resiliencein the adhesive material, a certain amount of relative rotation may bepermitted between the stack and the shaft under locked-rotor condition.This may be used to relieve strain which would otherwise break the gearsin the output of the tool or other device in which the motor is used. I

in another embodiment, the sleeve may be paper or cardboard ofsufficient thickness to provide the required dielectric strength. Inthis case, the adhesive layers need only be sufficientto insure bondingof the three elements of the structure together.

Regardless of the material selected, it is preferred that the arefilled. Of course, other insulative materials may be sleeve in theconstruction of this invention be a continuous cylindrical body. Whileit is possible toprovide multiple elements which, when placed togetherapproximate a cylinder, this introduces difficulty in aligning thepieces and therefore increases the cost and complexity of manufacture.In addition, the adhesive-may not adequately fill the interface betweenthe pieces and, even if it does, "it permits the possibility ofpropogation of a fault through one material, thus defeating aparticularly desirable feature of this. invention.

While several embodiments of .this invention have been shown anddescribed, it will be apparent to those skilled in the art that manychanges and modifications may be made from the specific illustrationswithout departing from the spirit of this invention in its broaderaspects as defined by the appended claims.

lclaimz- 1. An armature for an electric motor comprising a rotor havinga plurality of windings and a central bore;

a shaft located within said bore;

an insulating sleeve disposed between said rotor and said shaft;

a first adhesive layer disposed between said rotor and said sleeve toaffix rotor to said sleeve; and

a second adhesive layer disposed between said sleeve and said shaft toafiix said sleeve to said shaft.

2. An armature as claimed in claim 1 wherein said sleeve comprises acontinuous cylinder of insulating material.

3.. An armature as claimed in claim 2 wherein said sleeve alone hassufficient dielectric strength to insulate said shaft from saidwindings. l

4. An armature as claimed in claim 1 and including a stack 5. Anarmature as claimed in claim 4 wherein said sleeve comprises acontinuous cylinder of insulating material.

6. An armature as claimed in claim 1 wherein said adhesive layers aresufficiently flexible to protect said sleeve from stress fracture.

7. An armature as claimed in claim 6 wherein said sleeve is glass.

8. An armature as claimed in claim 1 wherein said sleeve is paper.

\ UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Pate t 3 ,789February 1 1972 Dated Thaddeus E. Bednarski Inventor(s) It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

AT COLUMN 4, LINE 23, BETWEEN "AI-"FIX" AND "Roma", SAID SHOULD BEINSERTED.

Signed and sealed this 17th day of October 1972.

(SEAL) Attest:

EDWARD M. PLETCHER,JR ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents Patent No. 3,639,789 Dated February 1, 1972 Thaddeus E.Bednarski Inventor(s) It is certified that error appears in theabove-identified patent and that said Letters Patent are hereby vcorrected as shown below:

AT COLUMN 4, LINE 23, scrwzm "AFFlx" AND "ROTOR", SAID SHOULD BE INSERTED.

Signed and sealed this 17th day of October 1972.?

(SEAL) Attest:

EDWARD M. PLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents

1. An armature for an electric motor comprising a rotor having aplurality of windings and a central bore; a shaft located within saidbore; an insulating sleeve disposed between said rotor and said shaft; afirst adhesive layer disposed between said rotor and said sleeve toaffix rotor to said sleeve; and a second adhesive layer disposed betweensaid sleeve and said shaft to affix said sleeve to said shaft.
 2. Anarmature as claimed in claim 1 wherein said sleeve comprises acontinuous cylinder of insulating material.
 3. An armature as claimed inclaim 2 wherein said sleeve alone has sufficient dielectric strength toinsulate said shaft from said windings.
 4. An armature as claimed inclaim 1 and including a stack of laminations between said sleeve andsaid windings, said windings being mounted on said laminations; andwherein said sleeve is at least as long as said stack.
 5. An armature asclaimed in claim 4 wherein said sleeve comprises a continuous cylinderof insulating material.
 6. An armature as claimed in claim 1 whereinsaid adhesive layers are sufficiently flexible to protect said sleevefrom stress fracture.
 7. An armature as claimed in claim 6 wherein saidsleeve is glass.
 8. An armature as claimed in claim 1 wherein saidsleeve is paper.